Industrial, utility, and military nuclear operations produce radioactive waste materials which must be treated in an appropriate manner before disposal to prevent environmental contamination. Additionally, as a result of recent treaties requiring the reduction of nuclear arsenals, development of procedures for disposal of weapons grade plutonium has assumed increasing urgency.
Because present technology does not provide satisfactory and economic conversion of the wastes' and weapons' radioactive nuclear components into non-radioactive nuclides, disposal of highly radioactive materials in geologic repositories remains the currently favored solution to the problem. However, because of the long half life of some radioactive nuclear species, the wastes must be stored in a form which minimizes the possibility of release.
In addition to the radioactive nuclear components of the wastes, the bulk wastes may also comprise or contain a variety of miscellaneous associated materials, such as rod assemblies, fuel containers, cladding, liners, and binders. These accompanying materials may or may not be radioactively contaminated, but they also require disposal if reuse or recycle thereof is not contemplated or feasible. Many of these extraneous materials are metal, and are not readily dissolvable in glass, the preferred storage medium.
Two particular types of waste, light-water reactor spent fuel and solidified high-level waste, have been considered well suited to repository disposal. Other types of spent nuclear fuel, e.g., miscellaneous spent fuels, have individual characteristics which have, until the invention herein, made disposal more difficult. Thus, many such fuels corrode or dissolve the containing media. Additionally, since the nuclear critical mass for some fuels is small, whatever method of disposal is adopted must prevent the fuel from becoming critical. In some cases, the spent fuel is encased in or at least partially surrounded by a metal cladding, such as a zirconium tube, which poses a major problem in the treatment of the fuel if dispersal or encasement in glass is contemplated. That is, metal claddings, as mentioned, normally do not dissolve in glass, and the metal may react with the components of the glass. Finally, the wastes must be disposed of in a form which is easily stored and safeguarded.
Current technology for solidifying high level radioactive waste involves heating the wastes, which consist primarily of radioactive actinides and fission products which have been processed into the form of nitrate salts, so that the nitrate wastes are destroyed with the formation of oxides and off-gases of water vapor and other minor gases. For this approach to be used, the wastes must be processed first into the nitrate form. The actinide and fission product oxides are then dissolved in a molten glass, and the glass containing the wastes is poured into containers, such as steel cylinders, and the glass is allowed to cool. The containers containing the waste are suitable for storage, the solidified glass being substantially impervious to chemical attack. While this procedure provides a suitable product for storage, the process creates disposal problems of its own.
In addition to the problems aforementioned, the disposal of weapons grade plutonium poses further difficulties. In particular, if the plutonium is not destroyed, it must be processed to a form which makes the plutonium inaccessible for nuclear weapons use. Accordingly, there has existed a need for the efficient processing of solid radioactive waste, particularly spent reactor fuel(s), and, more recently, for the treatment of weapons grade plutonium. The invention addresses these needs.